Mark Zuckerberg called Donald Trump to congratulate him on his shock 2016 election victory.

That's according to a new report from BuzzFeed News, which also says Facebook internally views the Trump campaign as an advertising "innovator."

Business Insider previously reported in May 2017 that Trump and Zuckerberg had spoken multiple times over the phone since the election.

Mark Zuckerberg called Donald Trump soon after the 2016 US presidential election to congratulate him on his shock victory, according to a new report from BuzzFeed News— and also reportedly congratulated him on his "successful [advertising] campaign on Facebook.

Mark Zuckerberg has made veiled criticisms of Trump, and has long championed political causes at odds with Trump's platform, like immigration reform. But the Trump campaign was also a major customer for Facebook's advertising business, spending $44 million in the run-up to the 2016 election.

According to documents obtained by BuzzFeed News, Facebook internally views the Trump campaign as an "innovator," and has gone on to use the campaign's techniques to refine its own advertising efforts.

While Zuckerberg and Trump have chatted behind the scenes, it's not clear if the pair have ever met face-to-face. In December 2016, Trump convened a meeting of high-profile tech executives including Apple's Tim Cook and Microsoft's Satya Nadella, but Facebook COO Sheryl Sandberg went instead of Zuckerberg.

Reached for comment, a Facebook spokesperson told Business Insider: "We declined to comment on the speculation to Buzzfeed and have nothing else to add."

Conservative politicians have claimed, without proof, that Facebook has an anti-conservative bias — but this hasn't dulled Trump operatives' taste for Facebook advertising. According to a recent study publicized in The New York Times, Trump and his Political Action Committee are currently the single biggest political advertiser on Facebook, spending $274,000 on adverts since May.